Click here to read a paper entitled "Telecom Convergence - A Historical Perspective." The paper is summarized below.
Roots of Convergence
In 1928, Harry Nyquist, a researcher at AT&T, published a paper that introduced the concept of characterizing a communications signal using discrete samples. This eventually led to the Nyquist Sampling Theorem, which states that a signal can be completely reproduced if the signal is sampled at a rate that is greater than twice the signal bandwidth. The implication of the Nyquist Sampling Theorem is that a band-limited signal can be represented and transmitted as a stream of bits. In other words all communications can be viewed as digital data communications.
Sampling at the Nyquist rate can result in very high data rates, so that in many cases, direct transmission of digitized samples is impractical. However in 1948, Claude Shannon, another AT&T researcher, published a paper that established the basis for data compression and efficient coding and digitizing of communication signals. Shannon's seminal paper presented a comprehensive theory of communications, which is referred to as "Information Theory." Information Theory implies that all types of communications are fundamentally the same and provides the theoretical basis for telecom convergence.
Missed Opportunities for Convergence
When Shannon's paper was published in 1948, transmission and switching technologies could not support an integrated network. However, over the following decades, transmission and switching technologies would improve dramatically. Unfortunately, the industry has been slow to exploit these technological advances, and opportunities for convergence have been missed.
One missed opportunity involved the use of cable TV networks to provide access to the backbone network. Coaxial cable (coax) provides a bandwidth that is more than sufficient to support convergence. By the 1970's, cable TV networks were widely deployed throughout the U.S., and digital communication technology was rapidly advancing. Telecom convergence based on cable access and a digital backbone was feasible. However, convergence did not happen, largely because of government regulations and restrictions.
Integrated Services Digital Network (ISDN) refers to an industry-wide effort to bring about telecom convergence. Narrowband N-ISDN, which was standardized in 1984, supported the convergence of voice and data communications. Broadband ISDN (B-ISDN) was an attempt at full convergence. In 1989, Asynchronous Transfer Mode (ATM) was adopted as the transport mechanism for B-ISDN. Although ATM achieved a certain degree of success in integrating voice and data communications, B-ISDN never really caught on and was overtaken by events.
Convergence Based on IP/MPLS
Multi-Protocol Label Switching (MPLS) is a technique that enables IP packets to be transported with a guaranteed quality of service. A consensus is forming around convergence based on MPLS transport of IP data.
Moving Beyond IP/MPLS
Convergence based on IP/MPLS is not the end of the road. Fast circuit switching can provide a transport efficiency that is comparable to the efficiency of IP/MPLS. Convergence based on fast circuit switching has some long term advantages over convergence based on IP/MPLS.